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Date: Wed, 12 Jun 2024 09:47:40 -0600
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Subject: Re: [PATCH net-next v10 02/14] net: page_pool: create hooks for
 custom page providers
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To: Jason Gunthorpe <jgg@ziepe.ca>, Mina Almasry <almasrymina@google.com>
Cc: Pavel Begunkov <asml.silence@gmail.com>, David Wei <dw@davidwei.uk>,
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From: David Ahern <dsahern@kernel.org>
In-Reply-To: <20240612120602.GQ791043@ziepe.ca>
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On 6/12/24 6:06 AM, Jason Gunthorpe wrote:
> On Tue, Jun 11, 2024 at 11:09:15AM -0700, Mina Almasry wrote:
> 
>> Just curious: in Pavel's effort, io_uring - which is not a device - is
>> trying to share memory with the page_pool, which is also not a device.
>> And Pavel is being asked to wrap the memory in a dmabuf. Is dmabuf
>> going to be the kernel's standard for any memory sharing between any 2
>> components in the future, even when they're not devices?
> 
> dmabuf is how we are refcounting non-struct page memory, there is
> nothing about it that says it has to be MMIO memory, or even that the
> memory doesn't have struct pages.
> 
> All it says is that the memory is alive according to dmabuf
> refcounting rules. And the importer obviously don't get to touch the
> underlying folios, if any.
> 

In addition, the io_uring developers should be considering the use case
of device memory. There is no reason for this design to be limited to
host memory. io_uring should not care (it is not peeking inside the
memory buffers); it is just memory references.

One of io_uring's primary benefits is avoiding system calls. io_uring
works with TCP sockets. Let it work with any dmabuf without concern of
memory type. The performance benefits the Google crowd sees with system
call based apps should be even better with io_uring.

Focus on primitives, building blocks with solid APIs for other
subsystems to leverage and let them be wired up in ways you cannot
imagine today.